1. Field of the Invention
The present invention relates to a cryopump and a method for regenerating the cryopump.
2. Description of the Related Art
A cryopump is a vacuum pump that traps and pumps gas molecules by condensing or adsorbing them on cryopanels cooled to ultracold temperatures. The cryopump is generally used to attain a clean vacuum environment required for a semiconductor circuit manufacturing process, for instance. The cryopump, which is a so-called entrapment vacuum pump, needs regeneration by which the trapped gas is periodically released to the outside.
It is known that, during regeneration, a first vacuum gauge is used when the pressure of a casing for the cryopump is low and a second vacuum gauge is used when the pressure thereof is high. The first vacuum gauge has a filament, whereas the second vacuum gauge does not have the filament. During regeneration, inflammable gas and combustion enhancing gas are released from cryopanels. When the pressure becomes high, the first vacuum gauge is turned off, so that the source of ignition can be eliminated.
In the above configuration, however, the release of gas from the cryopanels starts already before the first vacuum gauge is switched off. A risk that ignition occurs by accident remains plausible if the source of ignition and the inflammable gas coexist. For example, the heating of cryopanels for regeneration may start, inflammable gas adsorbed may be released at a rapid pace, or a combustible gas composition may be generated in the cryopump. It is not guaranteed that in such cases the first vacuum gauge has already been switched off.